1. Field of the Invention
The present invention relates to a thin film magnetic head, and more specifically it relates to a thin film magnetic head with improved write characteristics in the high frequency range.
2. Discussion of Background
An inductive electromagnetic transducer is employed to constitute the write element in a thin film magnetic head which is used in a magnetic disk device constituting a storage apparatus of a computer in the prior art. The inductive thin film magnetic transducer constituting the write element is provided with a first magnetic film, a second magnetic film, a gap film, a coil film supported by an insulating film and the like.
The front ends of the first magnetic film and the second magnetic film are respectively constituted of a first pole tip and a second pole tip that face opposite each other over the gap film having a very small thickness, and a write is performed at the first and second pole tips. The yokes of the first magnetic film and the second magnetic film are linked to each other to complete a magnetic circuit at a back gap portion that is located on the opposite side from the first and second pole tips. The coil film is formed to wind around the back gap portion in a coil.
An MR (magnetoresistive) element is employed to constitute the read element. The MR read element is capable of achieving a high degree of resolution regardless of its speed relative to the magnetic disk. The MR read element includes a first shield film, a second shield film and an MR element. The first shield film and the second shield film are provided over a distance from each other via an appropriate non-magnetic insulator, with the MR element provided between the first shield film and the second shield film.
In order to support high recording density using this type of thin film magnetic head, the quantity of data stored in memory per unit area of the magnetic disk (areal density) must be increased. An improvement in the areal density viewed from the thin film magnetic head is achieved through an improvement in the capability of the write element and by achieving a higher frequency at the write circuit.
In one of the means for improving the capability of the write element to improve the areal density, the length of the gap between the pole tips is reduced. In another means for improving the areal density, the number of data tracks that can be recorded in the magnetic disk is increased. The number of tracks that can be recorded in a magnetic disk is normally expressed as TPI (tracks per inch). The TPI capability of a write element can be improved by reducing the head dimensions that determine the data track width.
Various methods have been tried in the prior art as specific means for improving the areal density through an improvement in the write element capability. For instance, Japanese Unexamined Patent Publication No. 262519/1995 and Japanese Unexamined Patent Publication No. 225917/1995 disclose means for adjusting the width of the lower portion to the width of the second pole tip through ion beam milling.
Now, in order to achieve an improvement in the areal density through higher frequency at the write circuit, the maximum recording/reproducing frequency at a thin film magnetic head has been increased to as high as 100 MHz or higher in recent years. However, it has been learned that in such a high frequency range, the non-linear transition shift (hereafter referred to as NLTS) increases and that the overwrite characteristics (hereafter referred to as the O/W characteristics) deteriorate. NLTS refers to a phenomenon in which the write position shifts when a write is performed with data bits in close proximity on the magnetic recording medium. NLTS is explained in IEEE, TRANSACTIONS ON MAGNETICS vol. 27, No. 6, November, 1991, pages 5316 to 5318 and in IEEE, TRANSACTIONS ON MAGNETICS vol. 32, No. 1, January 1996, pages 61 to 66. As explained in these publications, when the degree of NLTS increases, various read systems are critically affected, for instance, the operating characteristics of a PRML (partial response maximum likelihood) read system.
To date, NLTS has been corrected through circuit means in this type of thin film magnetic head. However, NLTS can be corrected through a circuit-type method only up to 40%. When the geometric design means described above is adopted for the poles, NI,TS cannot be reduced to 40% or lower, which is required in practical use, in a high frequency range of 100 MHz or higher.